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You need to determine how the original gauge is wired. Is it a simple DC ammeter circuit, or is it one of the heated-wire gauges?
The gauge has three terminals: +12v, Sender, and GND.
To do this, with the gauge powered, I would first measure the open-circuit voltage between the sender terminal on the gauge and ground using a DMM.
Second, I would put my DMM in DCmA mode, and measure the current that flows from the sender terminal on the gauge to ground.
Third, I would connect a 70Ω resistance (68Ω+2.2Ω, or a pot set to read 70Ω) from the sender terminal on the gauge to ground, and measure the voltage between the sender terminal on the gauge and ground.
OK5.58v
I don't understand this. I expected a steady reading. Is it pulsing? Is the meter jumping between two stable readings?2.02 amps -> 0.01 amp
OK3.0v
I don't understand this. I expected a steady reading. Is it pulsing? Is the meter jumping between two stable readings?
At first the amps are 2.02 and then after 20 seconds the reading is a constant 0.01 amp.